This invention relates to a process for the production of fuels and lubricating base oils, and, more particularly, it relates to processes for the production of a full range of lubricating oils including high viscosity base stocks and transportation fuels in a single integrated hydrocracking system.
Hydrocracking a refinery stream to produce both fuels and lubricating oil products is a process having conflicting objectives. Fuels hydrocracking, particularly involving hydrocracking a feedstock boiling above the boiling range of the desired fuel, aims to crack a substantial portion of the refinery feedstock. It is desirable to reduce the molecular weight of virtually all of the refinery stream if possible, with substantial portion of the cracked products preferably boiling in the range of the desired fuel(s). In contrast, the ideal refinery stream suitable for use in preparing a lubricating oil product by hydrocracking boils in the range of the desired lubricating oil product, or at a slightly higher temperature. Hydrocracking removes the low boiling components of the refinery stream which are not desirable for the lubricating oil product, along with heteroatoms, while leaving the most desirable higher boiling components behind for inclusion with the lube product. The presence of some hydrocracking reaction products in the lubricating oil range are acceptable, so long as they do not predominate in any lubricating oil product fraction, and thereby unacceptably reduce the viscosity index of the lubricating oil product.
Conventional methods for producing both fuels and lubricating oil products from a single integrated hydrocracking system are optimized for one type of product, with the properties and yield of the second type of product being dictated by conditions imposed on the system. For example, a fuels hydrocracker, operated at high severity for producing fuels, may also have a lubricating oil product stream. However, the lubricating oil product recovered in this type of hydrocracking system is generally characterized by a low viscosity and often by a very high viscosity index. There is little flexibility in the type of lubricating oil product produced. Furthermore, feed to a fuels hydrocracker may be cracked numerous times through repeated recycle steps before being recovered. While repeated cracking operations are acceptable for fuels, such repeated operations are detrimental to lube properties. It is desirable to have a process for producing high yields of high quality fuels while maintaining the flexibility for selecting the desired product properties for lubricating oil product(s) recovered from the process.
Methods of producing high quality lube fraction from fuels hydrocracker bottoms have been attempted by others. The instant process is, however, directed to an integrated process for production of both fuels and lube oil products. U.S. Pat. No. 5,580,442 (Kwon et al) discloses a process in which an atmospheric residue is distilled in a first vacuum distillation unit to produce a vacuum gas oil(VGO). The VGO is hydrotreated to remove impurities, then hydrocracked. The light hydrocarbons created by cracking are then removed by distillation, and the unconverted oil is passed to a second vacuum distillation unit to produce lubes. The remaining material is then recycled to the hydrocracker.
WO 97/18278 (Bixel et al) also discloses a method for producing feedstocks of high quality lube base oil from unconverted oil of a fuels hydrocracker operating
In recycle mode. A vacuum distillation unit is employed following fractionation. Any of the fractions from the vacuum distillation unit may be recycled to the hydrotreater, passed to the hydrocracker, or sent to an FCC unit. The cuts from the vacuum distillation unit need not be recycled to the hydrocracker. Kwon et al does not disclose the necessity of operating the fuels hydrocracker to produce waxy fuels hydrocracker bottoms which have the appropriate hydrogen content to obtain subsequently dewaxed basestocks having a VI of at least 115, as does Bixel et al.
U.S. Pat. No. 5,985,132 (Hoehn et al) discloses a method for producing lube blending stocks by employing a lubes hydrocracker rather than a fuels hydrocracker, as used in the instant invention. A lubes hydrocracker employs a conversion level or less than 30%. One portion of the effluent stream is directly removed from the first hydrocracking zone to produce lube blending stocks. Another portion of the effluent stream from the first hydrocracking zone is directly introduced into a second hydrocracking zone without intermediate separation, and is cracked to produced fuels. In the instant invention the effluent from the first hydroprocessing zone passes to an atmospheric separation zone.
The present invention provides a process for hydrocracking a refinery stream to produce fuels, including naphtha, kerosene and diesel fuel, while maintaining the flexibility to recover one or more high quality lubricating oil product(s). The process further provides the flexibility for preparation of lubricating oil products having a wide range of viscosities and viscosity indices.
Thus, an objective of the present invention is to produce a high quality lube fraction from a fuels hydrocracker. Another objective of the present invention is to provide a full range of lube streams, over a wide viscosity range and a wide viscosity index range, from a fuels hydrocracker. Another objective of the present invention is to provide a high viscosity index lube stream from a fuels hydrocracker.
This invention illustrates an integrated process for producing both fuels and lubricating oil products from a single integrated hydrocracking system, which produces high yields of high quality fuels, while maintaining flexibility for selecting the desired product properties for the lubricating oil products recovered from the process, comprising the steps of:
a) contacting a liquid hydrocarbon feedstock with hydrogen over a first catalyst in a hydroprocessing zone which may be operated at either hydrotreating or hydrocracking conditions, which is operated at conditions effective to remove impurities contained in the feedstock, to yield a first effluent containing a normally liquid fraction;
b) separating the normally liquid fraction from the first effluent by boiling point range to yield at least a first lubricating oil product, a first fuel product and a bottom fraction;
c) contacting at least a portion of the bottom fraction with a second catalyst in a hydrocracking zone operated at conditions effective to hydrocrack the bottom fraction, to yield a second effluent;
d) separating the second effluent by boiling point range to yield an overhead stream and a recycle stream; and (e)recycling the recycle stream to the hydrocracking zone.
In the present invention, a lubricating oil product is separated from the effluent of a hydroprocessing zone, which may be operated at either hydrotreating or hydrocracking conditions. This zone is operated at conditions preselected to achieve a lubricating oil product having the desired properties. Portions of the effluent not recovered for lubes is then hydrocracked in a hydrocracking zone to produce fuel boiling range products at high yields.